Jessica and Siobhan: the party is over in Mistresses. Photograph: BBC/Ecosse Films

"Long time," snapped Siobhan, stomping past Katie in a cagoule the colour of dead trees. "I know," replied Katie, stiff-shouldered in an uneventful cardigan, her face a picture of misery. The message was clear: Mistresses has Gone Serious. What was once frivolous, glossy and summery is now contemplative, matte and autumnal. Where once there was rumpery, now there is only frumpery.

But weep ye not. The ingredients that made the first two series so brilliantly, stupidly addictive – the communal snarking about hopeless men over endless bottles of prosecco, the lingering shots of aspirational interiors, the frantic bums, tums and thighs workouts on designer faux-fur throws – may have been (temporarily?) replaced by more sombre concerns, but this was still an expertly crafted slab of premier soap. There were new enemies and old habits, fresh intrigues and genuinely quite exciting subplots. Meanwhile, simmering underneath it all was an inexorable sense of doom – a bubbling cauldron of disquiet that threatened to erupt, spraying the birch-veneer fittings with hot gobbets of Big Drama.

We joined the quartet two years after the events of the second series. Before we could ponder the reasons for their current estrangement (and what an estrangement – gathered reluctantly at Katie's house in rumpled leisurewear, the atmosphere between the former friends wasn't exactly happy hour at Wetherspoons), we were whisked back to six months earlier for a hearty serving of plot.

Mistresses: Trudi is cooking up trouble. Photograph: BBC/Ecosse Films

Siobhan is now a single mum nursing distinctly ambivalent feelings for the engaged-to-someone-else Dominic. Trudi's cake emporium (McGreggs) is up to its icing bag in debt, while her late-night spreadsheet sessions have incurred the frustration of thuddingly dull househusband Richard. Guilt over her treatment of Dan has forced Katie into both self-imposed singledom and a series of hitherto unthinkable cardigans. "I am on my own because frankly I don't know who would want me any more!" honked the locum, cableknit sleeves flapping, as her brittle mother (a splendidly crackly Joanna Lumley) gazed on, open-mouthed, across the duck-egg blue expanse of her distressed rustic kitchen.

As for Jessica, where to start? Gone are the days where the party planner's diary consisted solely of four-hour business lunches followed by a dash to the nearest boutique hotel with AN Hunk/Hunkess to play "sexy mortar and pestle" until the ensuing clouds of love-dust clogged up the air conditioning and she had to get room service in to clean it out with wet wipes. Instead, Jessica 2:0 now spends her time fretting about her finances with earnest husband Mark and drinking water (water!) in outdoor cafes before going all Bridges of Madison County over another negative pregnancy test ("I am trying to be brave and buoyant and, you know, JESSICA, but I just can't do it any more!"). And she's recovering from a miscarriage. It's all a bit glum.

The warp and weft of female friendship that underpins the series appears to have woven itself into a pattern of self-loathing. Everywhere you look there are signs reading "Impending financial disaster 15 miles" and "This way to catastrophic romantic imbroglio".

So, what did you make of it all? Has the Mistresses autumn/winter look added a welcome depth to the gloss? Or did you prefer it when the ladies spent their time making pigeon noises at shoes and banging their way through Bristol's seemingly inexhaustible supply of expressionless style-supplement wristwatch models? Over, as they say, to you…